Thank you for uploading this video, the initial ground footage is very interesting and to some degree is covered in the video added below from the Naval History and Heritage Command, Photographic Section, UV-1.
For accuracy purposes "only" there are a number of issues with this current Internet Archive "Inside The Enola Gay" video.
•Starting at 0:42
all of the Taxi, takeoff and in flight footage of the B-29 are not Enola Gay. This is denoted by the gun turrets on this (stand-in) aircraft; in flight, the turrets are a little harder to see in some frames, but the side blisters on the side of this standard B-29 are pretty clear. The Silverplate B-29's (nuclear capable variant) were stripped of side blisters and armament (four gun turrets), except for the tail Guns.
also hard to see I'm pretty confident that the bombardier here is not Thomas W. Ferebee, the bombardier on Enola Gay for the Hiroshima mission. Ferebee can be seen in the video added below if one freezes the video at 5:35
back row standing third from the left.
the bomb leaving the bomb bay is not Little Boy (LB). this is denoted by the tail on this bomb, as LB had a fully enclosed box tail; the weapon in this video has exposed tail fins. The tail design of LB can be seen in the video added below starting at 1:24
as LB is rolled out of the Tinian Bomb Assembly Building on 5 August 1945 (loading day).
All of the above brings into question the internal aircraft film footage and it is suspected this footage is also of a standard B-29 and not the Enola Gay or other Silverplate. It is unclear why the producers of this film (initially perhaps MED or AEC [unknown production date]; NARA: filed as Department of Energy (DoE) record group at the National Archives) would select a standard B-29 as a Stand-in for Enola Gay, perhaps little film footage of Silverplate's in flight or for security purposes.
This is by no means a critique of this upload; the intent here is to explain the inaccuracies of this film so viewers will understand that this is a "reenactment" of the Hiroshima mission with some (stand-in) in flight aircraft film footage.
Source: Naval History and Heritage Command, Photographic Section, UV-1. see http://youtu.be/VBP0IKaPZxI
Also see: "The Silverplate Bombers" By Richard H. Campbell (2005)